The Commission shall be empowered to adopt delegated acts, in accordance with Article 284, in order to determine:
(a)
the rules for the calculation of the amount of import or export duty applicable to goods for which a customs debt is incurred in the context of a special procedure, which supplement the rules laid down in Articles 85 and 86;
(b)
the cases referred to in Article 86(4);
(c)
the time-limit referred to in Article 87(2).